TFX program (which developed the F-111), was written along those lines. Combat during the Vietnam War demonstrated that the entire "Missileer" concept was not ready for real combat conditions. Restrictive rules of engagement (ROE), limitations in communications (IFF), unreliable missiles and a wide variety of other problems conspired to make air-to-air combat devolve into dogfights far more often than US air combat tacticians had envisioned. In spite of a huge technical superiority on paper and some very successful BVR missile aces, the F-4s found themselves fighting at close quarters with the so-called "inferior" Soviet-designed MiG-21, and losing the fight more often than expected. Heavy and poorly maneuverable fighters originally imagined by the F-X program would be even worse off in these situations. Boyd's work with E-M modeling demonstrated that the F-111 would be poorly suited to the role of fighter, and the Air Force F-X proposal was quietly rewritten to reflect his findings, dropping a heavy swing-wing from the design, lowering the gross weight from 60,000+ pounds to slightly below 40,000, and decreasing the top speed from Mach 2.7 to 2.3–2.5. The result was the F-15 Eagle, an aircraft that was far superior in maneuverability to the F-111 fighter variants. The Air Force had also been studying a lighter day fighter. Starting in 1965, the Air Force had pursued a low-priority study of the Advanced Day Fighter (ADF), a 25,000 pound design. After they learned of the MiG-25 in 1967, a minor panic broke out and the ADF was dropped in order to focus work on the F-15. The F-15, originally a lighter aircraft, grew in size and weight as it attempted to match the inflated performance estimates of the MiG-25. While Boyd's contributions to the F-15 were significant, he felt that it was still a compromise. Boyd, defense analysts Tom Christie, Chuck Myers, test pilot Col. Everest Riccioni and aeronautical engineer Harry Hillaker formed the core of the "Fighter Mafia" which worked behind the scenes in the late 1960s to pursue a lightweight fighter as an alternative to the F-15. The group strongly believed that an ideal fighter should not include any of the radar-guided missile systems, active radar or rudimentary ground-attack capability that found their way into the F-15. Riccioni coined the nickname, a joke on his Italian heritage that harkened back to the "Bomber Mafia" (whose acolytes still occupied the upper command positions of the Air Force)